This invention relates generally to valves and more particularly, but not by way of limitation, to high pressure communicating, low pressure actuated valves. The present invention also relates to set point pressure controllers utilizing such valves, particularly set point controllers for relieving pressure from high pressure autoclaves.
In the oil and gas industry cement slurries are pumped into well bores for various reasons, one of which is for cementing casing. Different well bores can have different temperature and pressure conditions which can affect different cement slurries; therefore, it is desirable to be able to test a particular cement slurry for its suitability for a particular well bore environment. Such testing is well known in the industry.
A typical cement test occurs in a closed container to which heat can be applied to heat a sample of the cement to a desired temperature. The contents of the closed container are also maintained under pressure. The temperature and pressure are typically those anticipated to be encountered downhole. This type of testing device includes autoclaves. Specific examples of such test equipment are the Halliburton Services Cement Consistometer and the Halliburton Services Ultra-sonic Cement Analyzer (UCA).
In such high pressure devices, there has been a need for a pressure limiting mechanism to limit pressure increases such as result from temperature increases brought about by the heating which is typically performed at the beginning of a test. This pressure limiting has been done by a technician monitoring a pressure gauge and manually opening a valve to relieve pressure. A preferable way would be to use a valve which would automatically release a limited volume of pressurized fluid from the test container to produce a drop in pressure when the pressure reaches a predetermined level. This would require a controllable relief valve, but relief valves which are rated at 20,000 pounds per square inch (psi), which is a typical pressure rating on cement testing equipment of the type mentioned hereinabove, are not common, and those presently available typically relieve a much larger volume than is acceptable to maintain sufficient pressure to continue the desired cement test in the example of the Halliburton Services Cement Consistometer or the Halliburton Services Ultra-sonic Cement Analyzer.
One valve which has a suitable pressure rating is one available from Autoclave Engineers. In a test using this valve, it was determined that the valve reaction time was not acceptable and that too much pressure was relieved from the small cement testing container such as is used in the aforementioned Cement Consistometer and Ultra-sonic Cement Analyzer. We also believe that the large mass of the piston and inherent friction of the packing seal of the Autoclave Engineer valve would be detrimental to the accurate control needed with the particular type of cement testing equipment referred to hereinabove.
For achieving accurate high pressure control of high pressure testing containers, such as consistometers and the like, a valve is needed which can respond quickly, release small volumes of pressurized fluid, and be used with high pressure fluids. To facilitate control, it would also be desirable for such a valve to have a small size and to respond to low pressure actuation. It would also be desirable for such a valve to be controllable by a computer. There is also the need for a set point pressure controller which includes and adapts such a valve for controlling pressure in a high pressure environment.